A conductive polymer is used in a wide variety of industrial fields including an electrolytic capacitor, an organic light-emitting diode, an antistatic film and a touch panel.
Polyaniline, one of conductive polymers, has advantages that, in addition to its electric properties, it can be synthesized easily from inexpensive aniline and show improved stability to oxygen or the like in a conductive state. Further, highly-conductive polyaniline can be obtained easily by a method mentioned in Patent Document 1. Here, the polyaniline composition disclosed in Patent Document 1 is a solution type polyaniline composition in which doped polyaniline is dissolved in a solvent.
However, the thermal resistance of the conductive polyaniline composition disclosed in Patent Document 1 is not necessarily high, and has a problem that the resistance thereof increases by about 10 times as compared with the initial value if it is allowed to stand in an inactive gas at 105° C. for 10 days, for example.
On the other hand, a dispersion type polyaniline composition in which doped polyaniline is not dissolved is also known. Further, it is known that heat resistance is improved by using sulfonic acid as a dopant (Patent Document 2). However, a dispersion type polyaniline composition has a defect that the resulting molded article is weak if solid matters thereof are composed only of polyaniline fine particles.
In order to solve this problem, it is also known to add a binder resin which is a solid matter other than polyaniline. However, since a binder resin is an insulator, another problem occurs that the conductivity of the resulting molded article is decreased.
Further, in a dispersion type polyaniline composition, since doped polyaniline fine particles are agglomerated and precipitated, when a molded article is produced by using this dispersion type polyaniline composition, a problem arises that this composition has to be mixed during the production to allow polyaniline fine particles to be dispersed in the composition.
It is also known that the heat resistance is increased by adding sulfonic acid to a dispersion type polyaniline composition (Patent Document 3). However, since the polyaniline composition disclosed in Patent Document 3 is of dispersion type, it suffers from the same problem as mentioned above. Further, a molded article produced by using a “conductive composition obtained by adding sulfonic acid to dispersion type polyaniline” disclosed in Patent Document 3 has a significantly lowered conductivity as compared with a molded article produced by using a “conductive composition obtained without adding sulfonic acid”.